Many receivers use some form of digital filtering for a variety of purposes including channel selection, channel rejection and interference rejection. The specific filtering requirements for individual scenarios are generally dynamic, for example for channel or interference rejection, and in these situations a dynamic filter allows optimum performance, for example how well an interferer is rejected, for the least complexity and/or power consumption.
In a broadband OFDM/CDMA system operating in the ISM band there are many sources of interference, one of which is narrowband frequency hopping systems. Adaptive filters can be used in CDMA applications where CDMA signals are interfered with by a narrowband jammer. In an article “Adaptive Digital Signal Processing JAVA Teaching Tool” by M. Hartneck and R. W. Stewart, submitted to IEEE Transactions on Education-Special CDROM Issue, November 1999, also available on the internet at: http://www.spd.eee.strath.ac.uk/users/bob/adaptivejava/begin.htm, there is disclosed an example of CDMA interference suppression in which if a broadband (stochastic) signal has interference from a narrowband (periodic) source a prediction architecture can be used to attempt to find correlation between an output y(k) of an adaptive filter and an input signal which has been fed forward from a delayed input of the adaptive filter. By taking the difference between the signals, viz. d(k)−y(k), the narrowband signal is attenuated and it is found that an output signal e(k) is approximately equal to the signal applied by a data source to the transmission channel. As a generality adaptive filters use error calculations in order to make minor adjustments to the filter coefficients. As the demands for high performance filtering grow there is an attendant problem of complexity and increased power consumption.